Microfluidics is inherently a domain where high performance cell and particle handling has proven to be very successful. Some of the ruling technology platforms, which are industrial and clinical standards for high quality cell processing, are found in the fluorescence activated cell sorter (FACS) (Fluorescent detection and sorting) and in the Coulter Counter (size distribution measurements). The combination of fluorescently labeled cell specific antibodies and the FACS technique opened the route to a revolution in modern cell biology. However, all problems could still not be solved by that technique, such as sorting specific cells from a population of cells wherein no marker is used and thereby there are no biomolecular modifications or other perturbation of the cells.
Extensive studies have explored passive hydrodynamic techniques to separate cells and particles such as deterministic lateral displacement, hydrodynamic filtration, hydrophoretic separation and pinched flow fractionation. These techniques are solely dependent on the fluid dynamic properties of the separation channel in relation to the particle size. These techniques commonly display good separation properties but suffer from low throughput as particle concentration has to be low in order to achieve good separation. To overcome these problems a number of alternative approaches including split thin flow fractionation, magnetophoresis, optical methods as well as dielectrophoresis have been investigated. A common feature of these approaches is that particles/cells are separated by means of an applied force field directed transversely to the direction of the general flow direction in order to cause selective deflection of particle/cell trajectories. However, all these techniques have so far not managed to separate cells with a high degree of particle/cell discrimination and/or at particle throughputs that are sufficient for a broad applicability in life science applications. Acoustophoresis has also been shown to perform particle/cell separation by the use of acoustic force fields acting on particles in suspension. Acoustophoresis suffers to a less extent of throughput limitations, nor is it highly dependent of ionic strength or pH as compared to e.g. dielectrophoretic techniques.
A common problem when using microchannels for separation of species in aqueous suspensions is that of dispersion, due to the laminar flow conditions, associated with small length scales. The laminar flow implies that the fluid velocity (u) in the length direction (x) of such a channel depend on the spatial position relative to the channel width (y-direction) and height (z-direction). Near the walls the velocity approaches zero while in the bulk, the flow velocity is higher. Hence, the retention time in the channel for a particle/cell will, in effect, be dictated by its initial lateral position (y and z). I.e. cells/particles entering at different positions in the transverse cross section of the channel will pass through the channel at different speed. Separation can only be truly deterministic if particles/cells enter the separation channel in the exact same lateral position, and thereby flow through the separation channel at equal speed. Thus the particle/cell position at the end of such separation channel is a function of the initial position of the particle/cell and the employed external force field.
A prerequisite to fulfill the requirement for a deterministic separation outcome is that cells/particles are pre-aligned in the yz-plane of the fluid flow prior to entering into the channel region which encompasses the actual separation step. Pre-alignment can be accomplished by employing external forces in two dimensions along the y- and z-axis.
US2009/0042310 discloses the separation of particles by the use of an acoustic force, wherein said acoustic force is a one dimensional force applied two times to separate cells, wherein they are moving particles in a flow rate.
Mannebeg O et al., J of micromechanics and microengineering, 2008, 18, page 1-9 discloses how one dimensional forces in both the x and the y axis.
Several strategies have been proposed to isolate circulating tumor cells (CTCs) such as physical e.g. physical structures in the channel that captures the tumor cells, and biochemical affinity based approaches involving microbeads or micro-posts. To date, most successful techniques to enrich CTCs from metastatic cancer patients depend on immuno-labeling. Epithelial cells in general, and the majority of epithelial derived tumor cells express the epithelial cell adhesion protein (EpCAM) and different cytokeratines (CK), which are absent in normal blood cells. These markers are vastly used in the available CTC isolation methods. However, a drawback is the exclusion of EpCAM or CK negative CTCs. The substantial variations in both morphology and antigen expression among CTCs consequently call for innovative approaches to enhance CTC enrichment. The invention is focused on the above defined drawbacks with the systems.